1. Field of the Invention
The present invention relates to a system for error classification and error handling in a hierarchical storage management system.
2. Description of the Related Art
Computer users today require ever increasing amounts of data storage to run complex applications, such as those involving digital imaging, multimedia, and video-on demand. These applications require massive amounts of data space to store files. Storage systems for non-volatile, long term storage of digital data include, magnetic tapes, magnetic hard disk drives, optical disks, holographic storage, etc. As the cost of magnetic hard disk drive space decreases, one solution is to use magnetic hard disk drives for long term data storage. Magnetic hard disk drives are preferred as they provide higher data transfer and access rates than other storage devices, such as magnetic tape cartridges, optical disks, etc.
Notwithstanding, there are many administrative labor costs associated with installing, configuring and managing hard disk drives. Furthermore, a large amount of data residing on hard drives is inactive. In fact, it is estimated that only twenty percent of information stored on a network is accessed during the course of a month. One solution is to store more frequently used data on hard disk drives and periodically back-up less frequently used data to magnetic tape such that the more frequently used data is resident on the hard disk drives. Such a system takes advantage of the low cost of tape drives and tape media to archive less frequently used data and at the same time maintain more frequently used data available on the faster, yet costlier, hard disk drives. Maintaining less frequently used data on slower hard disk drives will likely have a negligible effect on system users. The benefits of providing a primary storage of hard disk drives and a secondary storage comprised of a less expensive, and typically slower media, is further discussed in "ADSTAR Distributed Manager (ADSM)--Hierarchical Storage Management (HSM) White Paper (IBM Document No. G522-24322-00, International Business Machines, 1996), which is incorporate herein by reference in its entirety.
International Business Machines Corporation (IBM) developed the ADSTAR Distributed Storage Manager (ADSM) to provide hierarchical storage management (HSM) over data storage devices. The concept of HSM is to transparently migrate infrequently accessed data automatically from more costly, higher performance storage devices, such as hard disk drives, to less expensive, slower storage devices such as tape drives and optical libraries. In the ADSM system, when a primary storage device, such as a hard disk drive directly accessible to users, reaches a predetermined threshold, the least frequently used files are migrated to tape storage. The migrated files on the hard disk drive are replaced with a small stub file identifying the location of the migrated file on the tape drive. The stub file would present information on the file name and other characteristics to system users browsing the hard disk drive. Thus, to system users, the stub file appears to be the complete migrated file. When a system user accesses the stub file, the ADSM would recall the file represented by the stub file from the tape archive and copy it to the local hard drive to make the data available to system users. In this way, tape storage provides seamless and unlimited disk space which is accessible at all times to system users as if the data was always resident on the local hard disk drive.
Various system errors may arise when a server attempts to transfer data between secondary storage, such as a tape cartridge, and primary storage, such as a local hard disk drive. In many prior art systems, the server provides only limited information on the access error. For instance, the IBM AIX version for ADSM provides only minimal error information in the form of the ENOTREADY error code. The ENOTREADY code indicates that the tape system was not ready for operation or the tape was not loaded in the drive. Moreover, in prior art systems, if an error occurs when a tape drive is accessed during operations, the user must contact a human system administrator to diagnose and handle the error.